#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl
inline int power(int a, int b) {
    int x = 1;
    while (b) {
        if (b & 1) x *= a;
        a *= a;
        b >>= 1;
    }
    return x;
}


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

//_ ***************************** START Below *******************************




vector<int> a;
vector<int> b;

bool isPossible(int n, int k, double mid){
	vector<double> t(n);
	for(int i=0; i<n; i++){
		t[i] = a[i] - b[i]*mid;
	}
	
	sort(begin(t), end(t), greater<double>());
	
	double sum = 0;
	for(int i=0; i<k; i++){
		sum += t[i];
	}
	
	return sum >= 0;
	
}

double consistency(int n, int k){

	double s = 0;
	double e = INF;
	
	for(int i=0; i<100; i++){
		double mid = s + (e-s)/2;
		if(isPossible(n, k, mid)){
			s = mid;
		}
		else e = mid;
	}
	
	return e;

}

















double practice(int n, int d){
	
	return 0;
	
}





void solve() {

    int n, k;
    cin>> n >> k;
    a.resize(n);
    b.resize(n);

    for(int i=0; i<n; i++){
        cin >> a[i];
        cin >> b[i];
    }
    
	cout << fixed << setprecision(7) << consistency(n, k) << endl;
	
	// cout << fixed << setprecision(7) << consistency(n, k) << " -> " << practice(n, k) << endl;
    
    

}





int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int t = 1;
    while (t--) {
        solve();
    }

    return 0;
}